Leibfried, in U.S. Pat. Nos. 4,900,779, 4,902,731, 5,013,809, and 5,077,134, Bard and Burnier, in U.S. Pat. Nos. 5,008,360 and 5,068,303, and Burnier, in U.S. Pat. No. 5,025,048, describe crosslinked organosilicon polymers and crosslinkable organosilicon prepolymers comprised of polycyclic hydrocarbon residues and cyclic polysiloxanes or siloxysilane residues linked through carbon to silicon bonds, and processes useful for preparing the same. Cowan, in U.S. Pat. No. 4,877,820, and Burnier, in U.S. Pat. No. 5,025,048, disclose crosslinked or crosslinkable linear poly(organohydrosilane) polymers having at least 30% of their .tbd.SiH groups reacted with hydrocarbon residues derived from polycyclic polyenes. The crosslinked polymers have the desirable characteristics of high glass transition temperature (Tg), low dielectric constant, and low moisture absorption, in addition to other desirable properties. The polymers and prepolymers are useful for electronic applications, such as preparing printed circuit boards (including substantially tack-free prepreg and laminates useful for preparing such circuit boards) and encapsulated electronic components, and structural applications.
All of the above-listed patents are hereby incorporated in their entirety, by reference thereto.
U.S. Pat. Nos. 4,900,779 and 4,902,731 state that the thermoset polymers are fire retardant and burn very slowly when subjected to flame. In addition, these patents state that the organosilicon polymers described therein are tough thermoset polymers which pyrolyze upon heating to a temperature greater than 1000.degree. C. and that this high temperature resistance makes these polymers useful as refractory materials, fire resistant materials, and ablative materials.
While some of the above polymers are fire retardant in that they eventually extinguish when removed from a flame, they are not sufficiently fire retardant (do not self extinguish quickly enough) to meet standards required for many electronic applications.
Accordingly, it is an object of the invention to provide an organosilicon composition that self extinguishes quickly enough to meet fire retardant standards required for electronic applications.
It is also an object of the invention to provide an organosilicon composition that self extinguishes quickly enough to meet fire retardant standards required for electronic applications, and also has properties desirable for electronic applications such as high glass transition temperature (Tg), low dielectric constant, and low moisture absorption.
It is another object of the invention to provide such flame retardancy properties to the organosilicon compositions without adversely affecting processing conditions for forming such organosilicon compositions, for instance without substantial degree of inactivation of the catalyst.
It is a further object of the present invention to provide an organosilicon prepolymer having improved storage stability.